"You have to see how it will be be viewed by society at large. It is subjective, but we still need to draw that line somewhere."
Plates were not issued if they promoted violence, discrimination, bias, illegal substances or activities, or encouraged unsafe driving. They must also not be derogatory to the police or public figures, breach intellectual property rights or contain bad language.
Mr Plates director Bruno Szajer runs a website that trades thousands of number plates in New Zealand and Australia.
Szajer said he had not heard of the MH370-related plates, and thought they were "a bit shocking".
The sale of plates related to world events — both joyful and tragic — was common, he said.
However, the most common personalised plate purchases remained those related to new cars, especially expensive models.